DE102007024166A1 - Metal substrate for a superconducting thin-film strip conductor - Google Patents

Abstract

A high-temperature superconducting thin-film strip conductor comprising a metal substrate, a buffer layer chemically produced thereon and a superconducting coating chemically produced thereon is characterized by high texturing of the buffer layer if the metal substrate has a surface roughness rms <50 nm, preferably rms <10 nm, and the buffer layer has grown directly, without an intermediate layer, crystallographically unrotated with respect to the crystalline structure of the metal substrate on its surface.

Description

The The invention relates to a high temperature superconducting thin film ribbon conductor and in particular its metal substrate.

High-temperature superconducting thin-film band conductors, in the following Coated Conductors, hereinafter HTSC-CC, are produced according to the prior art starting from a textured metal strip. The strip, referred to below as the metal substrate, consists of a metal which preferably crystallizes face centered in a cubic manner (eg Ni, Cu, Au). Particularly suitable is nickel, in particular nickel with a few at% tungsten, cf. DE 101 43 680 C1 , The textured metal substrate is coated with a buffer layer which serves to transfer the texture of the metal substrate to the superconducting layer subsequently produced in a known manner. Particularly suitable for the buffer layer are materials having a low lattice mismatch with both the metal substrate and the crystalline, high temperature superconducting thin film. Both materials that are rotated by 45% on the metal substrate are used, eg. As lanthanum and other materials with fluoride or pyrochlore, as well as those that grow unrotated and often perovskite, z. Strontium titanate and calcium titanate, or spinel structure, e.g. Strontium ruthenate and neodymium nickelate.

Out "Effect of sulfur on cube texture formation in microalloyed nickel substrate tapes" (J. Eickemeyer et al.), Physica C 418 (2005) 9-15 . "Sulfur superstructures for texture optimization" (C.Cantoni et al.), IEEE Transactions at Applied Superconductivity, Vol. 13, No. 2, "Growth of oxide seed layers on Ni and other technologically interesting metal substrates. 2003 and other publications it is known that a chalcogenide superstructure, in particular a sulfur superstructure, which normally forms from impurities of the metal substrate, favors the epitaxial growth of buffer layers which are deposited by means of a physical method, in particular by vapor deposition of the metal substrate in a high vacuum. Therefore, in the prior art, the goal is pursued to reproducibly produce as uniform a superstructure as possible with a high degree of coverage. However, the physical deposition of the buffer layer is a costly process, which is therefore not suitable for the production of HTSC-CC or even their carrier substrate.

Also known and much cheaper is the production of HTSC-CC by means of chemical coating method (CSD / MOD), cf. "Chemical solution deposition of <100> oriented SrTiO3 buffer layers on Ni substrates"; JT Dawley et al., J. Mater. Res., Vol. 17, No.7, 2002 , Good results have been obtained on Ni substrate with sulfur superstructure on which lanthanum zirconate is grown, cf. "Detailed investigations on La2Zr207 buffer layers for YBCO coated conductors prepared by chemical solution deposition" (Knoth K. et al.), Acta Materialica 55, 2007, 517-529 ,

comparable However, results can be obtained with materials that are not like Lantanzirkonat rotated by 45 °, but grow up unrotated, z. Strontium titanate, not achieve, uzw. even if, as is known, a metal substrate with low surface roughness was used. The applied strontium titanate layers are untextured or only slightly textured.

Of the Invention is based on the object produced by a chemical route HTSC-CC with highly textured buffer layer and in particular a Metal substrate as a starting material available for this to deliver.

This succeeds according to the invention by the in the claim 1 specified method, in which one has a superstructure of the surface of the metal substrate before applying the Buffer layer removed.

Surprisingly It has been shown that a superstructure in particular a chalcogenide superstructure and above all a sulfur superstructure, which by means of physical Methods generated buffer layers and by means of chemical processes produced buffer layers with fluoride or Pyrochloridstrutkur necessary, in the case of a chemical coating with unrotated growing materials such as those with perovskite or spinnell structure on the contrary prevents the formation of a good texture.

This Result is both of the type of removal of the superstructure (mechanical polishing, electropolishing, blasting with blasting, z. B. dry ice particles or selective etching with weak concentrated nitric acid) as well as the type of chemical coating technology, ie spin coating, Dip-coating or printing (slot-die-casting, ink-jet-printing) as independent as from the parameters of the following Process such as annealing temperature, atmosphere and holding time.

The best results are obtained when the substrate in the course of Removal of the superstructure to a surface roughness of less than 10 nm is polished.

Advantageous For the buffer layer, a material is used whose Lattice constant of that of the metal substrate less than ± 15%, preferably less than ± 10%, deviates.

in the Further, the invention relates to the use of a biaxial textured metal substrate having the features specified in claim 8.

The Buffer layer may in particular consist of a material whose Lattice constant of that of the metal substrate by less than ± 15%, preferably deviates less than ± 10%. In particular, come however, materials in which the lattice constant is different from those of the metal substrate in the range of -5% to + 15%.

The Invention thus provides a high temperature superconducting thin film ribbon conductor with the features of claim 10 available.

Especially suitable as a metal substrate is nickel or a nickel alloy, containing 85 at%, preferably 90 at% nickel. In this Case are suitable as buffer layer materials, especially titanates, Ruthenates, manganates, nickelates, and cuprates, e.g. CaTiO3, La2NiO4, Sr2RuO4, NdBa2Cu3Ox, Gd2CuO4, SrTiO3, Nd2CuO4, BaTiO3, (CaxSr1-x) TiO3 and (Srx Ba1-x) TiO3.

Examples:

It were two different Ni (5 at% W) metal substrates of the company evico used (belt width 10 mm, belt thickness 80 μm). These Metal substrates both had a cube texture (001) half-width (FWHM) of 5.5 °.

Both Substrates were subjected to equal roll forming and then recrystallized in a batch annealing process. By slow Cooling in the batch annealing process formed Both substrates from a sulfur superstructure.

• Substrat 1: rms = 40 nm
• Substrat 2: rms = 5 nm

The roughness of the two metal substrates was measured by AFM microscope as follows:

• Substrate 1: rms = 40 nm
• Substrate 2: rms = 5 nm

• Substrat 1 (poliert): rms = 5 nm

A part of the substrate 1 was mechanically polished. The polishing took place on a polishing table (Struers) with a 0.1 μm diamond suspension. The roughness of the substrate could be reduced by the polishing to rms = 5 nm. Polishing removes all adherent surface layers, including the sulfur superstructure. Since no annealing was done before the coating, this structure could not be replicated.

• Substrate 1 (polished): rms = 5 nm

All Substrates were sonicated first with acetone and then cleaned with isopropanol for 5 min each.

• Substrat 1: rms = 40 nm; Schwefelüberstruktur
• Substrat 2: rms = 5 nm; Schwefelüberstruktur
• Substrat 3: rms = 5 nm; keine Schwefelüberstruktur, d. h. Substrat 1, jedoch poliert

The following substrates were therefore available for the following experiments:

• Substrate 1: rms = 40 nm; Sulfur superstructure
• Substrate 2: rms = 5 nm; Sulfur superstructure
• Substrate 3: rms = 5 nm; no sulfur superstructure, ie substrate 1, but polished

• Lösung 1: reines Strontiumtitanat (STO)
• Lösung 2: Nb-dotiertes STO, elektrisch leitend
• Lösung 3: Ca-dotiertes STO, bessere Gitteranpasssung zu Ni Substrat

Three coating solutions were prepared:

• Solution 1: pure strontium titanate (STO)
• Solution 2: Nb-doped STO, electrically conductive
• Solution 3: Ca-doped STO, better lattice matching to Ni substrate

For solution 1, 0.15 mol of Ti (OCH 2 CH 2 CH 2 CH 3) 4 were dissolved in acetylacetone in a molar ratio of 1: 2. Subsequently, 0.15 mol of Sr acetate were dissolved in glacial acetic acid in a molar ratio of 1: 5. Both solutions were combined and diluted to 500 ml with a mixture of glacial acetic acid and methoxyethanol such that the total ratio of glacial acetic acid and methoxyethanol was 1: 2. The solution was then filtered over possibly precipitate to be removed. The ICP-OES analysis (SPECTRO Genesis) gave a stoichiometric 0.3 molar solution.

For Solution 2 was 0.1425 moles of Ti (OCH 2 CH 2 CH 2 CH 3) 4 in acetylacetone dissolved in a molar ratio of 1: 2 and with 0.0075 mol Nb (OCH 2 CH 3) 5 dissolved in butanol. All further Steps were performed as for solution 1, so that a 0.3 molar coating solution for a strontium titanate with 5% Nb doping was obtained.

solution 3 was prepared as solution 1, but instead of 0.15 mol Sr acetate a mixture of 0.135 mol Sr acetate and 0.015 mol Ca acetate used. It became a 0.3 molar coating solution for a Ca-substituted strontium titanate.

All purified substrates were coated with all solutions as follows:
The cleaned substrates of 5 cm in length were first coated on a spin coater at 500 / min with a coating solution diluted by a factor of 6. The dilution was carried out with a 2: 1 mixture of glacial acetic acid and methoxyethanol. Subsequently, the temperature treatment was carried out under 10% H2 in N2 at a temperature of 800 ° C for 5 min. The dilution of the solutions produced in the first coating step a so-called seed layer, ie a discontinuous layer (coverage between 20-80%) whose islands act as nucleation nuclei for subsequent layers.

Under the same conditions were followed by two more coatings and Temperature treatments, but with undiluted solutions. The resulting total layer thickness was included after 3 coatings 250 nm in each case. The layer thickness was transferred by means of a profile meter measured a layer edge.

tries for varying the annealing temperature between 750 and 900 °, and the glow atmosphere between 5-15 H2 in N2 showed no significant influence on the test result. When using a dip coating system All solutions must be at a coating speed of 10 m / h by a factor of 2 to be the same results to reach. Higher dive speeds require less Dilutions.

For the 3 substrates the following results for solution 1 (STO) were observed:
As a measure of the texture, the ratio I was used from 200 (32 °) to 110 (47 °) reflex. From a value of about 5, a good texture can be assumed. Substrate 1 Substrate 2 Substrate 3 I (200) / I (110) 1 2 6

Result:

The Removal of sulfur superstructure in substrate 3 improved with the same surface roughness as substrate 2 the texture the buffer layer threefold.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 10143680 C1 [0002]

Cited non-patent literature

• "Effect of sulfur on cube texture formation in microalloyed nickel substrate tapes" (J. Eickemeyer et al.), Physica C 418 (2005) 9-15 [0003]
• - "Growth of Oxide seed layers on Ni and other technologically interesting metal substrates: issues related to formation and control of Sulfur superstructures for texture optimization" (C. Cantoni et al.), IEEE Transactions on Applied Superconductivity, Vol 13, No. 2 , 2003 [0003]
• "Chemical solution deposition of <100> oriented SrTiO3 buffer layers on Ni substrates"; JT Dawley et al., J. Mater. Res., Vol. 17, No.7, 2002 [0004]
• - "Detailed investigations on La2Zr207 buffer layers for YBCO coated conductors prepared by chemical solution deposition" (K.Knoth et al.), Acta Materialica 55, 2007, 517-529 [0004]

Claims (12)

A method for processing a biaxially textured metal substrate as a starting material for a high-temperature superconducting thin-film strip conductor (HTSC) consisting of the metal substrate, a buffer layer chemically generated thereon, crystallographically unrotated with respect to the metal substrate, and then a chemically generated superconducting coating, characterized in that a superstructure of the metal substrate is removed before the generation of the buffer layer. Method according to claim 1, characterized in that that a chalcogenide superstructure is removed. Method according to claim 1 or 2, characterized that the metal substrate to a surface roughness rms <50 nm, preferably rms <20 nm, especially it prefers rms <10 nm, is processed. Method according to one of claims 1 to 3, characterized in that the superstructure by Polishing is removed. Method according to one of claims 1 to 4, characterized in that for the buffer layer, a material is used, the lattice constant of derjeni conditions of the metal substrate less than ± 15, preferably less than ± 10%, differs. Method according to one of claims 1 to 5, characterized in that the metal substrate after removal the superstructure is cleaned. Method according to Claim 6, characterized that the metal substrate is cleaned in an ultrasonic bath. Method according to claim 6 or 7, characterized that the metal substrate enfettet us, in particular using of acetone and isopropanol. Use of a biaxially textured metal substrate without superstructure and with a surface roughness rms <50 nm, preferably rms <20 nm, especially preferably rms <10 nm, as a starting material for a high-temperature superconducting Thin-film strip conductor (HTSC-CC) consisting of a metal substrate, a chemically generated, crystallographically unrotated opposite the buffer layer grown on the metal substrate and thereon one chemically generated superconducting coating. Use of a metal substrate according to claim 9, wherein the buffer layer consists of a material whose lattice constant from that of the metal substrate by less than ± 15%, preferably less than ± 10%, deviates. High-temperature superconducting thin-film strip conductor (HTSC-CC), consisting of a metal substrate, one on it chemically generated buffer layer and then a chemically generated, superconducting Coating, characterized in that the metal substrate is a Surface roughness rms <50 nm, preferably rms <20 nm, especially preferably rms <10 nm, and that the buffer layer immediately, without interlayer, Crystallographically unrotated towards the crystalline Structure of the metal substrate grown on its surface is. Metal substrate for one of the preceding Claims, characterized in that it is at least 85 at%, preferably 90 at% nickel.